EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: drakejest on January 06, 2021, 05:40:46 am
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Hello I would like to customize my current transformer SCT-013 burden resistor to be similar to 20A : 1V version. What i have is the 100A : 50mA version and i know enough that the difference between the voltage and current version is a burden resistor inside the current transformer. Since i can easily buy those SMD resistors inside i rather modify the current version that i have than to pay expensive shipping for the 20A : 1V voltage version.
I think they all use the same number turns of the coil so judging from the 100A : 50mA i can extrapolate that
20A : 10mA by doing ratio and proportion
In order for me to get a voltage output i use ohms law
R = V/I
R = 1V/0.01A
R = 100 Ohms
Am I correct ??
So basically i do the same for every other value i want for example if i want an awkward value like 16A : 1v i do the same by first R&P sooo
100A : 50 mA = 16A : 8mA
R = 1V / 0.008A
R = 125
Am i doing this correctly?
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A current transformer is a special case of a transformer. In this case, it is a step-up transformer, the primary winding of the current one turn of the power wire passing through.
Its special parameter is the current transfer coefficient. In this case, the output current is indicated for short-circuit, for direct connection the ammeter.
The calculation of 20A:1V may be incorrect, there may be a different combination of the number of turns of the secondary winding and the load resistor.
To get the voltage, not the current, you need to install a load resistor. You calculated it correctly for 100:0.05. Just do not forget that at 100A you will get 6.25V, more current will not work because of the saturation of the transformer.
P.S. Never leave the pins of a current transformer flying. Without load, there can be multiple kV.
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Just do not forget that at 100A you will get 6.25V, more current will not work because of the saturation of the transformer.
All their versions when i opened them up contained what looks to be a bidirectional diode along with the burden resistor so i shouuld be safe at the same time the line im measuing with has a beake rating of 16A so there is another security there
I could not find a current transfer coefficient on the datasheet expemt for a 1:1800 turn ratio and 1 % linearity soo i guess should work ?
but to truely be sure i guess i have to test it
the only hard part is finding a current source, i guess ill have to coil some wire and use a shunt resistor to measure the current
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Just do not forget that at 100A you will get 6.25V, more current will not work because of the saturation of the transformer.
All their versions when i opened them up contained what looks to be a bidirectional diode along with the burden resistor so i shouuld be safe at the same time the line im measuing with has a beake rating of 16A so there is another security there
I could not find a current transfer coefficient on the datasheet expemt for a 1:1800 turn ratio and 1 % linearity soo i guess should work ?
but to truely be sure i guess i have to test it
the only hard part is finding a current source, i guess ill have to coil some wire and use a shunt resistor to measure the current
Yes, using a load resistor for a current transformer is common, it should work.
As a load for testing, if you do not have other means, it is not bad to use 55/110W car lamps. The current can be measured in a circuit break with a multimeter, it can be adjusted using a laboratory power supply, in fact, the current value of the current most power supplies demonstrate with some error. It will probably be enough for you to make several measurements at different currents to check the linearity.